Conventionally, there has been proposed a power supply system, which is used in combination of a solar battery as a distributed power supply and a storage battery (e.g., JP 2002-171674 A (hereinafter, referred to as “Document 1”)). This type of power supply system has an advantage that a power converter can be used in common by the solar battery and the storage battery. Document 1 discloses a technique of causing excess electric power generated by the solar battery to reversely flow into an electrical grid, and preventing electric power stored in the storage battery from flowing out to the electrical grid.
In recent years, there has been developed a fuel battery, which generates electric power, using hydrogen obtained by reforming fuel gas. In addition, there has been also proposed a cogeneration device, which uses, for heating water, the heat caused by the fuel battery in generating of the electric power. In many cases, it is proposed that the fuel battery as the cogeneration device is singly used, or in combination with the solar battery. On the other hand, there are only a few examples where this type of fuel battery is further combined with a distributed power supply in which the solar battery is combined with the storage battery.
In particular, in the configuration of using the fuel battery only for purpose of compensating for power shortage, it may be impossible to obtain a sufficient heat quantity for supplying hot water because of a small amount of power generated by the fuel battery. As a cogeneration device other than the fuel battery, there has been also known a configuration of using gas engine.